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Research Publications (Engineering and Built Environment)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/215

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End date: 2007Subject: search.filters.subject.Optimal design

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    A method for optimally designing laminated plates subject to fatigue loads for minimum weight using a cumulative damage constraint
    (Elsevier, 2000) Walker, Mark
    A procedure to optimally design laminated plates for a specific cyclic life using a cumulative damage constraint is described. The objective is minimum weight, and the design variables are the fiber orientation, and the plate thickness. The plates are subjected to cyclic bending loads, and the finite element method, in conjunction with the Golden Section method, is used to determine the design variables optimally. The FE formulation is based on Mindlin theory for moderately thick laminated plates and shells, and the formulation includes bending–twisting coupling. In order to demonstrate the procedure, several plates with differing events, load magnitudes and type, aspect ratios, boundary conditions and cyclic lives are optimised, and compared.
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    A computational methodology to select the best material combinations and optimally design composite sandwich panels for minimum cost
    (Elsevier, 2002) Walker, Mark; Smith, Ryan E.
    A procedure to select the best material combination and optimally design sandwich laminates with fibre reinforced skins and low density cores for minimum cost is described. Sandwich constructions generally provide improved stiffness/mass ratios and provide more tailoring opportunities than monolithics, and thus greater chance of satisfying design constraints. The objective of the optimisation is to minimise the laminate cost by selecting the skin and core material combination, layer thicknesses and skin fibre angles optimally, subject to load and mass constraints. As the optimisation problem contains a number of continuous (ply angles and thicknesses) and discrete (material combinations) design variables, a sequential solution procedure is devised in which the optimal variables are computed in different stages. The methodology and its benefits are demonstrated using graphite, glass or kevlar/epoxy facings, and balsa or PVC cores.
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    A technique for optimally designing fibre-reinforced laminated plates under in-plane loads for minimum weight with manufacturing uncertainties accounted for
    (Springer, 2006) Walker, Mark; Hamilton, Ryan Jason
    A procedure to design symmetrically laminated plates under buckling loads for minimum mass with manufacturing uncertainty in the ply angle, which is the design variable, is described. A minimum buckling load capacity is the design constraint implemented. The effects of bending–twisting coupling are neglected in implementing the procedure, and the golden section method is used as the search technique, but the methodology is flexible enough to allow any appropriate problem formulation and search algorithm to be substituted. Three different tolerance scenarios are used for the purposes of illustrating the methodology, and plates with varying aspect ratios and loading ratios are optimally designed and compared.
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    Optimal design of symmetric laminates with cut-outs for maximum buckling load
    (Elsevier, 1999) Walker, Mark
    Finite element solutions are presented for the optimal design of symmetrically laminated rectangular plates with central circular cut-outs subject to a combination of simply supported, clamped and free boundary conditions. The design objective is the maximisation of the biaxial buckling load by determining the fibre orientations optimally with the effects of bending–twisting coupling taken into account. The finite element method coupled with an optimisation routine is employed in analysing and optimising the laminated plate designs. The effect of plate size and boundary conditions on the optimal ply angles and the buckling load are numerically studied, and these results are compared to those from an article which appeared in this journal in 1996; viz. plates without cut-outs (Walker M, Adali S, Verijenko VE. Optimisation of symmetric laminates for maximum buckling load including the effects of bending–twisting coupling.
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    A methodology for optimally designing fibre-reinforced laminated structures with design variable tolerances for maximum buckling strength
    (Elsevier, 2005) Walker, Mark; Hamilton, Ryan Jason
    A procedure to design symmetrically laminated structures for maximum buckling load with manufacturing uncertainty in the ply angle—which is the design variable, is described. It is assumed that the probability of any tolerance value occurring within the tolerance band, compared with any other, is equal, and thus the technique is aimed at designing for the worst-case scenario. The finite element method is implemented and used to determine the fitness of each design candidate, and so the effects of bending–twisting coupling are accounted for. The methodology is flexible enough to allow any appropriate finite element formulation and search algorithm to be substituted. Three different tolerance scenarios are used for the purposes of illustrating the methodology, and plates with varying aspect and loading ratios, as well as differing boundary conditions, are chosen to demonstrate the technique, and optimally designed and compared.
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    A technique for optimally designing engineering structures with manufacturing tolerances accounted for
    (Taylor & Francis, 2007) Tabakov, Pavel Y.; Walker, Mark
    Accurate optimal design solutions for most engineering structures present considerable difficulties due to the complexity and multi-modality of the functional design space. The situation is made even more complex when potential manufacturing tolerances must be accounted for in the optimizing process. The present study provides an in-depth analysis of the problem, and then a technique for determining the optimal design of engineering structures, with manufacturing tolerances in the design variables accounted for, is proposed and demonstrated. The examples used to demonstrate the technique involve the design optimization of simple fibre-reinforced laminated composite structures. The technique is simple, easy to implement and, at the same time, very efficient. It is assumed that the probability of any tolerance value occurring within the tolerance band, compared with any other, is equal, and thus it is a worst-case scenario approach. In addition, the technique is non-probabilistic. A genetic algorithm with fitness sharing, including a micro-genetic algorithm, has been found to be very suitable to use, and implemented in the technique. The numerical examples presented in the article deal with buckling load design optimization of an laminated angle ply plate, and evaluation of the maximum burst pressure in a thick laminated anisotropic pressure vessel. Both examples clearly demonstrate the impact of manufacturing tolerances on the overall performance of a structure and emphasize the importance of accounting for such tolerances in the design optimization phase. This is particularly true of the pressure vessel. The results show that when the example tolerances are accounted for, the maximum design pressure is reduced by 60.2% (in the case of a single layer vessel), and when five layers are specified, if the nominal fibre orientations are implemented and the example tolerances are incurred during fabrication, the actual design pressure could be 64% less than predicted.